Embodiments described herein relate generally to electrochemical cells having semi-solid electrodes that have damage tolerance such that the electrochemical cells can be subjected to mechanical or thermal damage without substantial degradation in electronic performance and/or experiencing thermal runaway.
Batteries are typically constructed of solid electrodes, separators, electrolyte, and ancillary components such as, for example, packaging, thermal management, cell balancing, consolidation of electrical current carriers into terminals, and/or other such components. The electrodes typically include active materials, conductive materials, binders and other additives.
Some known methods for preparing batteries include coating a metallic substrate (e.g., a current collector) with slurry composed of an active material, a conductive additive, and a binding agent dissolved or dispersed in a solvent, evaporating the solvent, and calendering the dried solid matrix to a specified thickness. The electrodes are then cut, packaged with other components, infiltrated with electrolyte and the entire package is then sealed.
Such known methods generally involve complicated and expensive manufacturing steps such as casting the electrode and are only suitable for electrodes of limited thickness, for example, less than 100 μm (final single sided coated thickness). These known methods for producing electrodes of limited thickness result in batteries with lower capacity, lower energy density and a high ratio of inactive components to active materials. Furthermore, the binders used in known electrode formulations can increase tortuosity and decrease the ionic conductivity of the electrode.
Damage to conventional li-ion batteries, for example, li-ion batteries that include conventional electrodes, can negatively impact the electronic performance of the battery and in some instances, can even cause catastrophic failure. Damage can include mechanical damage, for example, bending, crushing, impact, shock, vibration, or penetration, or thermal damage, for example exposure to high or low temperatures or excessive temperature cycling. Such damage can affect the electronic performance of the battery, for example, increase impedance, reduce energy density and/or charge capacity of the battery. In some cases, such damage can cause over heating of the battery and/or short circuit (e.g., internal or external short circuit) which can lead to accelerated release of gases, and drying out of the electrolyte. Heat generated can be greater than the heat dissipated by the battery which can eventually lead to excessive heat build up in the battery. This is called thermal runaway which, in some cases, can cause the battery to explode or catch fire. In some cases, physical damage can cause the liquid electrolyte in the battery to leak out and burn causing the battery to catch fire or explode.
Physical damage is of particular concern for hybrid and plug-in electric vehicle manufacturers that use li-ion battery packs as the primary or secondary power source. If such a vehicle is involved in an accident, the li-ion cells within the battery pack, for example li-ion cells formed from conventional electrodes, can be damaged and undergo catastrophic failure. In 2011, the Chevy Volt plug-in hybrid became a target of an investigation by the National Highway Traffic Safety Administration (NHTSA) because the battery pack included in the Chevy Volt caught fire when subjected to a crash test. This clearly underscores the need for new li-ion battery technologies which are damage tolerant.
Thus, it is an enduring goal of energy storage systems development to develop new electrochemical batteries and electrodes that have longer cycle life, increased energy density, charge capacity and overall performance, and are relatively safe when subjected to mechanical or thermal damage.